1. Field of the Invention
The present invention relates to a semiconductor device having a MEMS (Micro-Electro-Mechanical Systems) element with an actuator.
2. Description of the Related Art
In recent years, development of MEMS (Micro-Electro-Mechanical Systems) elements having a movable structure formed by micromachining is progressing on an extensive scale.
Typical examples of MEMS elements are a variable capacitor, switch, sensor, gyroscope, and mirror device. The MEMS elements include a piezoelectric MEMS element using a piezoelectric material which deforms upon receiving a voltage.
U.S. Pat. Nos. 6,359,374 and 6,355,498 disclose examples of piezoelectric MEMS elements functioning as a variable capacitor. Each of the actuators of U.S. Pat. Nos. 6,359,374 and 6,355,498 includes an upper electrode, lower electrode, and a piezoelectric film sandwiched between the upper electrode and the lower electrode. The actuator is moved by adjusting the voltage applied to the upper and lower electrodes of the actuator. The capacitance is changed by changing the distance between the upper electrode and the lower electrode of the variable capacitor.
However, in the structures described in U.S. Pat. Nos. 6,359,374 and 6,355,498, the piezoelectric layer is not flat because of a step. For this reason, when a voltage is applied to the electrodes on the upper and lower sides of the piezoelectric film, the piezoelectric film stretches nonuniformly, or the horizontal stretch of the piezoelectric film decreases. In addition, when the actuator moves, a crack may be formed at the step portion of the piezoelectric film, resulting in a decrease in yield.
As described above, in the conventional piezoelectric MEMS element, since the piezoelectric film is not flat, the reliability of the MEMS element is low.